Alloys



20 When at least one of the elements zinc or man- Patented Feb. 25, 1936 UNITED STATES PATENT OFFICE ALLOYS No Drawing. Application January 4, 1934, Serial No. 705,288

2 Claims. (01. 75-4) Magnesium base alloys containing tin and cobalt, the balance being substantially all magnesium, are disclosed and claimed in my copending application, Serial No. 705,285, filed concurrently herewith. The present invention resides in the discovery that magnesium-cobalt-tin alloys may be further improved by the addition of one or both of the elements manganese or zinc.

Magnesium-tin-cobalt alloys are characterized by very desirable mechanical properties, particularly, good tensile strength and elongation. Such alloys, as disclosed in my above-mentioned copending application, may contain from about 0.1 per cent to about 20.0 per cent of tin and from about 0.1 per cent to about 4.0 per cent of cobalt.

ganese is added to the aforesaid magnesium-tincobalt alloys their tensile strength is further improved and they remain amenable to still greater improvement on being subjected to suitable thermal treatments. The zinc may be added in amount between about 0.1 per cent and 10.0 per cent, and the manganese between about 0.1 per cent and 2.0 per cent.

A magnesium base alloy consisting of 1.0 per cent of cobalt and 5.0 per cent of tin had a tensile strength, in the sand cast condition, of 18,890 pounds per square inch and an elongation of 5.2 per cent in two inches. To this alloy I have added, for example, 4.0 per cent of zinc with the result that the tensile strength increased to 23,370 pounds per square inch and the elongation to 5.8 per cent in two inches. By a thermal treatment of 22 hours at 480 centigrade the tensile strength was raised to 28,700 pounds per square inch and the elongation to 10.0 per cent in two inches. The alloy was then given an additional aging treatment of 20 hours at 150 centigrade, after which it had a tensile strength of 32,700 pounds per square inch and an elongationof 6.5 per cent in two inches. -As a preferred alloy of this nature I use about 5.0 per cent of tin, 1.0 per cent of cobalt, and 4.0 per cent of zinc, thebalance being substantially all magnesium.

Manganese is the full equivalent of zinc in a number of respects pertaining to the magnesiumtin-cobalt alloy. For instance, I have found that they are similar in that, singly or in combination, they improve the corrosion resistance of these alloys. Likewise manganese and/or zinc vcentigrade.

raise the hardness, tensile strength and proportional limit of magnesium-cobalt-tin alloys. -For these reasons I use either of them singly or both of them in combination in these alloys although I prefer to restrict the total amount of man'ga- 5 nese and zinc to less than 10.0 per cent.

A magnesium base alloy containing about 5.0 per cent of tin and 0.5 per cent of cobalt had in the sand cast condition a tensile strength of 18,940 pounds per square-inch and an elongation of 5.7 per cent in two inches. This alloy after a thermal treatment of 19 hours at 525 centigrade had a tensile strength of 23,680 pounds per square inch and an elongation of 8.8 per cent in two inches. By adding to this alloy 4.0 per cent 5 of zinc and 0.4 per cent of manganese the heattreated strength increased to 31,200 pounds per square inch and the elongation to 11.0 per cent in two inches and after aging the tensile strength went up to 34,470 pounds per square inch and the 20 elongation dropped to 3.2 per cent. Generally speaking, the effect of artificial aging after a solution treatment is to raise the hardness, tensile strength, and'yield point and lower the elonga tion as in the last quoted example.

A magnesium base alloy containing 5.0 per cent of tin, 0.25 per cent of cobalt, 0.4 per cent of man- ,ganese, and 4.0 per cent of zinc had a tensile strength of 27,100 pounds per square inch and an elongation of 7.7 per cent in two inches after a thermal solution" treatment of 16 hours at 470 The alloy, in this heat-treated condition, was given an accelerated corrosion test under severe corrosive conditions, comprising alternate immersion in, and removal from, a bath of an aqueous solution of 3 per cent sodium chloride. After hours of this treatment the tensile strength was 27,670 pounds per square inch and the elongation 8.8 per cent in two inches. There is no particular significance to the fact that the properties actually improved during the test, the increase being attributable either to the ordinary experimental variation or to a slight aging effect. The significant point to be noted is that there was no appreciable decrease in properties under the attack of the corrosive reagent.

Another magnesium base alloy containing 0.5 per cent cobalt, 5.0 per cent of tin, 4.0 per cent of zinc, and 0.4 per cent of manganese had, after a solution treatment of if hours at 470 centigrade, a tensile stren of 31,200 pounds per square inch and an elongation of 11.0 per cent in two inches. Some of the heat-treated specimens were given the accelerated corrosion test described in the next precedingparagraph. and on 55 being tested had a tensile or 30,650v poundsper square inch and an elongation of 11.3 per cent in two inches. This variation again comes within the experimental variation.

As a preferred alloy of the tin-*cobalt-manganese type I use about 5.0 per cent 01' tin, 1.0 per cent of cobalt; and 0.4 per cent of manganese, balance substantially all magnesium. Ii manganese and zinc are simultaneously present I use about 4.0 per cent of zinc and 0.4 per cent of manganese.

Thealloys disclosed herein may be cast and extruded over the whole range disclosed and may. be forged, or otherwise mechanically deformed, when the amount of added alloying elements does not assume too great a proportion of the whole alloy.

'aosim In this specification and the appended claims the term magnesium base alloy signifies an alloy containing more than 50 per cent nesium.

I claim: l. A magnesium base alloy containing from about 0.1 per cent to about 20.0 per cent oi! tin,

of magfrom about 0.1 per cent to about 4.0 per cent of 

